JP2017014181A - Method for flashing reaction medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing acetic acid, in which methyl iodide concentration is maintained in the vapor product stream formed in a flashing step.SOLUTION: A method for producing acetic acid comprises: conducting separation in a flash vessel into a liquid recycle and a vapor product stream, wherein the vapor product stream comprises less than 24-36 wt% of methyl iodide concentration, 0.005-1 wt% of acetaldehyde concentration, 45-75 wt% of acetic acid, 9 wt% or less of methyl acetate, 15 wt% or less of water, and 1 wt% of hydrogen iodide with respect to total weight of the vapor product stream; and distilling the vapor product stream in a first column to obtain an acetic acid product stream and an overhead stream, wherein the acetic acid product stream comprises acetic acid and 300 wppm or less of hydrogen iodide and/or 0.1-6 wt% of methyl iodide, and the overhead stream comprises methyl iodide, water and methyl acetate.SELECTED DRAWING: None

Description

  [0001] The present invention relates to a process for the production of acetic acid, and more particularly to an improved process for flushing crude acetic acid product in an acetic acid production system.

  [0002] One of the most commercially useful methods of synthesizing acetic acid currently employed is carbonylation of methanol with carbon monoxide using a catalyst. This method is taught in US Pat. No. 3,769,329, the entire content of which is incorporated herein by reference. The carbonylation catalyst includes a metal catalyst such as rhodium and a halogen-containing catalyst promoter such as methyl iodide, and the metal catalyst is dissolved or dispersed in a liquid reaction medium or supported on an inert solid. This reaction is performed by continuously bubbling carbon monoxide gas in a liquid reaction medium in which a catalyst is dissolved.

  [0003] Methanol and carbon monoxide are fed to the reactor as raw materials. A portion of the reaction medium is continuously removed and fed to a flash vessel where the product is flushed and sent as vapor to the purification system. The purification system removes “light” or low-boiling components as overhead, resulting in a sidedraw stream that is subjected to further purification. The purification system may further comprise a column that dehydrates the side draw stream or removes “heavy” or high boiling components such as propionic acid from the side draw stream. In the carbonylation process to produce acetic acid, it is desirable to minimize the number of distillation operations to minimize the energy used in this process.

  [0004] US Pat. No. 5,416,237 discloses a process for producing acetic acid by carbonylation of methanol in the presence of a rhodium carbonylation catalyst, methyl iodide, and an iodide salt stabilizer. Maintaining a finite concentration of water in the liquid reaction medium of about 10% by weight or less and a methyl acetate concentration of at least 2% by weight while passing the liquid reaction medium through the flash zone to produce a vapor fraction, The vapor fraction is fed to a single distillation column where the acetic acid product is recovered by removing the acetic acid product. This vapor fraction contains up to about 8% by weight of water, acetic acid product, propionic acid by-product, and most of methyl acetate and methyl iodide.

  [0005] US Pat. No. 7,820,855 discloses a carbonylation process for producing acetic acid. The method comprises (a) carbonylating methanol or a reactive derivative thereof in the presence of a Group VIII metal catalyst and a methyl iodide promoter to produce a liquid reaction mixture comprising acetic acid, water, methyl acetate, and methyl iodide. (B) supplying the liquid reaction mixture to a flash vessel maintained at a reduced pressure at a predetermined supply temperature; and (c) simultaneously evaporating the reaction mixture while heating the flash vessel to produce a crude product vapor stream. In this method, the reaction mixture is selected, the flow rate of the reaction mixture supplied to the flash vessel is controlled, and the amount of heat supplied to the flash vessel is controlled to control the temperature of the crude product vapor stream. Is maintained at a temperature less than 90 ° F. relative to the temperature at which the liquid reaction mixture is fed to the flash vessel, and the acetic acid concentration in the crude product vapor stream is To be higher than 70% by weight of. The acetic acid product and most of the lighter fractions (methyl iodide, methyl acetate and water) are separated from the reactor catalyst solution by passing through a flash vessel, and the crude process stream is flushed with dissolved gas in a single-stage flash or purification section. Send to. The methyl iodide concentration decreases as the temperature of the flash vessel increases and the flow rate decreases.

  [0006] US Pat. No. 9,006,483 discloses a method for producing acetic acid for liquid-liquid separation of overhead from a distillation column for the purpose of reducing hydrogen iodide concentration. Distill the mixture containing hydrogen iodide, water, acetic acid and methyl acetate in the first distillation column to form an overhead and side or bottom stream containing acetic acid, then cool and condense the overhead in the condenser Acetic acid is produced by separating into an upper phase and a lower phase with a decanter. According to this method, the mixture has an effective water concentration of not less than an effective amount and not more than 5% by weight (for example, 0.5 to 4.5% by weight), and a methyl acetate concentration of 0.5 to 9% by weight (for example, 0.5 to 0.5%). 8% by weight) is fed to the distillation column, and the mixture is distilled to form a region having a high water concentration above the mixture supply position in the distillation column. Methyl iodide and acetic acid can be produced by reacting hydrogen iodide with methyl acetate in a region where the water concentration is high.

  [0007] There is a need for an improved method of acetic acid production with improved separation processes, increased production capacity, and reduced operating costs.

  [0008] In one aspect, the invention provides for removing the reaction medium from the reactor, flushing the reaction medium with a liquid recycle stream, 45-75 wt% acetic acid, 24-36 wt% iodination. Separating into a steam product stream comprising methyl, up to 9 wt% methyl acetate, up to 15 wt% water, 0.005-1 wt% acetaldehyde, and up to 1 wt% hydrogen iodide; And at least a portion of the vapor product stream is distilled in an acetic acid product stream comprising acetic acid and 300 wppm or less hydrogen iodide, preferably 50 wppm or less hydrogen iodide, and methyl iodide, water, and methyl acetate. A method for producing acetic acid comprising obtaining an overhead stream. In a preferred embodiment, the steam product stream comprises 55-75 wt% acetic acid, 24-35 wt% methyl iodide, 0.5-8 wt% methyl acetate, 0.5-14 wt% water, 0 0.01 to 0.8 wt% acetaldehyde, and 0.5 wt% or less hydrogen iodide. In another preferred embodiment, the vapor product stream comprises 60-70 wt% acetic acid, 25-35 wt% methyl iodide, 0.5-6.5 wt% methyl acetate, 1-8 wt% water. 0.01 to 0.7% by weight of acetaldehyde, and 0.1% by weight or less of hydrogen iodide. In addition to the low concentration of hydrogen iodide contained in the acetic acid product stream, the vapor product stream also contains 0.1 to 6% by weight methyl iodide and 0.1 to 6% by weight methyl acetate. Also good. The water concentration in the acetic acid product stream is maintained at 1-9% by weight.

  [0009] In one aspect, the liquid recycle stream comprises 0.01-0.5 wt% metal catalyst, 5-20 wt% lithium iodide, 10-2500 wppm corrosive metal, 60-90 wt%. Acetic acid, 0.5-5 wt% methyl iodide, 0.1-5 wt% methyl acetate, 0.1-8 wt% water, 0.0001-1 wt% acetaldehyde, and 0.0001- Contains 0.5 wt% hydrogen iodide.

  [0010] The overhead stream from the first column (eg, light fractionator) may be phase separated to form a light liquid phase and a heavy liquid phase. The light liquid phase comprises 1 to 40 wt% acetic acid, 10 wt% or less methyl iodide, 1 to 50 wt% methyl acetate, 40 to 80 wt% water, 5 wt% or less acetaldehyde, and 2 wt% % Of hydrogen iodide may be contained. The light liquid phase is 15-25 wt% acetic acid, 1-5 wt% methyl iodide, 1-10 wt% methyl acetate, 60-75 wt% water, 0.1-0.7 wt% It may be more preferable to contain acetaldehyde and hydrogen iodide of 0.001 to 0.5% by weight.

  [0011] In another embodiment, the present invention provides a reaction medium removed from the reactor in a flash vessel with a liquid recycle stream, 45-75 wt% acetic acid, 24-36 wt% methyl iodide, 9 wt% Separating into a steam product stream comprising the following methyl acetate, 15 wt% or less water, 0.005 to 1 wt% acetaldehyde, and 1 wt% or less hydrogen iodide; Acetic acid comprising distilling at least a portion of the product stream to obtain an acetic acid product stream comprising acetic acid and 0.1 to 6 weight percent methyl iodide and an overhead stream comprising methyl iodide, water, and methyl acetate. It is a method of manufacturing.

  [0012] In other embodiments, the invention provides 45-75 wt% acetic acid, less than 24-36 wt% methyl iodide, 9 wt% or less methyl acetate, 15 wt% or less water, and 1 wt% Distilling a mixture comprising hydrogen iodide to form an overhead stream comprising methyl iodide and a side withdrawal stream comprising acetic acid, and condensing the overhead stream to form a separate liquid phase A method for producing acetic acid. The mixture may contain 0.005 to 1% by weight of acetaldehyde. In one aspect, in the side withdrawal stream, the water concentration is maintained at 1-3 wt% and the hydrogen iodide concentration is maintained at 300 wppm or less.

[0013] The invention will be more fully understood from the accompanying non-limiting drawings.
[0014]
It is the schematic which shows acetic acid manufacture based on this invention.

Introduction
[0015] The production of acetic acid by methanol carbonylation involves forming a reaction medium in a reactor and flushing the reaction medium in a flash vessel to form a liquid recycle stream and a vapor product stream. The vapor product stream is then distilled in one or more distillation towers to remove by-products and form an acetic acid product. The present invention provides a method for producing acetic acid while suppressing the formation of by-products by maintaining the methyl iodide concentration in the vapor product stream formed in the flash step at a specific value. Methyl iodide is a useful promoter for carbonylation catalysts. However, during separation, methyl iodide tends to concentrate with the acetic acid separated from the reaction medium, so it is separated and returned to the reaction medium, avoiding significant losses due to fugitive release, and acetic acid product There is a need to reduce iodide impurities therein. The present invention reduces the amount of methyl iodide that must be recovered from the steam product stream while maintaining the methyl iodide concentration at a sufficient level in the steam product to increase production rates. Decreasing the amount of methyl iodide has the advantage that the amount of methyl iodide that must be separated is reduced, thereby eliminating the obstacles to the distillation column. If the obstacle of the distillation tower is removed, there is an advantage that the production capacity is increased and the operation cost is reduced. In addition to increasing production capacity, maintaining methyl iodide in the steam product at the desired level has a positive effect on the concentration of hydrogen iodide in the downstream distillation column, resulting in lower hydrogen iodide levels. However, there is an advantage that corrosion is suppressed.

  [0016] In one aspect, the steam product stream is less than 24-36% by weight methyl iodide, such as 24-35% by weight methyl iodide, more preferably 25-35% by weight, based on the total weight of the steam product stream. % Methyl iodide. As shown in US Pat. No. 7,820,855, the production rate decreases as the methyl iodide concentration based on the mass flow rate from the reactor to the flash vessel decreases. An object of the present invention is to maintain a high production rate without causing a decrease in mass flow rate as described in US Pat. No. 7,820,855.

  [0017] If the methyl iodide concentration is less than 24% by weight, the production rate decreases, which is not desirable. On the other hand, if the methyl iodide concentration of the steam product stream is 36% by weight or more, the load on the distillation column necessary for removing methyl iodide increases, which affects the production capacity. Methyl iodide cannot be excluded by the steam product stream. Maintaining the methyl iodide concentration in the vapor product in the range of less than 24-36% by weight is important for controlling the formation of hydrogen iodide by hydrolysis of methyl iodide. Hydrogen iodide is a known corrosive compound, but is undesirable because the concentration of methyl iodide in the vapor product stream can be over 36% by weight. Therefore, hydrogen iodide can be controlled as desired when methyl iodide in the steam product stream is less than 24% by weight to less than 36% by weight.

  [0018] The vapor product may be sampled using on-line measurement techniques to measure methyl iodide content, and feedback may be provided in real time or near real time. Online vapor product stream sampling is easier than sampling a liquid reaction medium. Further, the methyl iodide concentration in the vapor product is correlated with the methyl iodide concentration in the reactor, and indirectly indicates the methyl iodide concentration in the reactor. The ability to maintain a constant methyl iodide concentration in the steam product stream is beneficial in setting a schedule for adding methyl iodide to the reactor. For example, in commercial methods, small amounts of methyl iodide are lost due to fugitive emissions and the use of various exhaust streams in the separation system. If the methyl iodide concentration in the vapor product is reduced, more methyl iodide may be added to the reactor. Conversely, if the methyl iodide concentration is too high, a portion of the heavy liquid phase from the light fractionator may be removed from the system.

  [0019] In addition to methyl iodide, the vapor product stream also includes acetic acid, methyl acetate and water. By-products such as hydrogen iodide, acetaldehyde, propionic acid may also be present in the vapor product stream. The reactants, i.e. methanol and carbon monoxide, may be recovered in the steam product stream if not consumed. In one aspect, the steam product stream comprises 45-75% by weight acetic acid, 24-36% by weight methyl iodide, 9% by weight or less methyl acetate, and 15% by weight or less, based on the total weight of the steam product stream. Of water. More preferably, the steam product stream comprises 55-75 wt% acetic acid, 24-35 wt% methyl iodide, 0.5-8 wt% methyl acetate, and 0.5-14 wt% water. . In a further preferred embodiment, the steam product stream comprises 60-70 wt% acetic acid, 25-35 wt% methyl iodide, 0.5-6.5 wt% methyl acetate, and 1-8 wt% water. Including. The acetaldehyde concentration in the steam product stream is 0.005 to 1% by weight, for example 0.01 to 0.8% by weight, or 0.01 to 0.7% by weight, based on the total weight of the steam product stream. Also good. In some embodiments, acetaldehyde may be present in an amount less than 0.01% by weight. In addition to acetaldehyde, other permanganate reducing compounds ("PRC") such as acetone, methyl ethyl ketone, butyraldehyde, crotonaldehyde, 2-ethylcrotonaldehyde, 2-ethylbutyraldehyde, and aldol condensates thereof may be used. May exist. When these compounds are present in the vapor product stream, they are generally in an amount equal to or less than the acetaldehyde concentration. The steam product stream may comprise hydrogen iodide in an amount of 1% by weight or less, such as 0.5% by weight or less, or 0.1% by weight or less, based on the total weight of the steam product stream. It is preferred that the steam product stream is substantially free of propionic acid, i.e., the amount of propionic acid included is less than 0.0001% by weight relative to the total weight of the steam product stream.

  [0020] The present invention also has the advantage of easily maintaining the water balance in the separation system, particularly by controlling the net production of water during the distillation process. As a result, the present invention has the advantage of suppressing or preventing an increase in moisture and reducing the need to drain water from the system. Water discharge also has the disadvantage that it can lead to the loss of catalyst promoters such as methyl iodide. In exemplary embodiments, the increase in the net production of water in the distillation process is less than 0.5%, such as less than 0.1%, or 0, relative to the water concentration in the steam product stream fed to the distillation process. .05% or less. In contrast, US Pat. No. 9,006,483 describes promoting a reaction leading to the formation of water, and water is further added to the distillation step. The promotion of these reactions and the addition of water are expected to increase the net production of water and increase the load on the distillation apparatus.

  [0021] The steam product stream is supplied to a distillation column such as a first column (sometimes referred to as a light fractionator). In one optional aspect, a portion of the steam product stream may be condensed. In the first column, the vapor product stream may be separated to form an overhead stream, a product stream, and a bottom stream may be formed as required. The acetic acid product stream may be withdrawn as a side withdrawal stream, more preferably as a liquid side withdrawal stream. In one aspect, the acetic acid product stream contains primarily acetic acid and may contain water, methyl iodide, methyl acetate, or hydrogen iodide. It is preferred that the acetic acid product stream withdrawn into the side withdrawal stream comprises greater than 90%, such as greater than 94% or 96% by weight acetic acid, based on the total weight of the side withdrawal stream. In terms of range, the acetic acid product stream contains 90-99% by weight acetic acid, for example 91-98% by weight. At such concentrations, the bulk of the acetic acid fed to the first column can be removed to the side draw stream for further purification. There may be a small amount of acetic acid in the overhead or bottom of the first column, but it is preferred not to recover acetic acid as a product there.

  [0022] The method of the present invention comprises the step of maintaining the water concentration in the side withdrawal stream at 1 to 9 wt%, such as 1 to 3 wt%, more preferably 1.1 to 2.5 wt%. Is preferred. The hydrogen iodide concentration in the side withdrawal stream may be 300 wppm or less, such as 100 wppm or less, or 50 wppm or less. In terms of range, it is preferred that the side withdrawal stream comprises 0.05 to 300 wppm, such as 0.1 to 50 wppm, or 5 to 30 wppm hydrogen iodide, based on the total weight of the side withdrawal stream. Hydrogen iodide is soluble in an acetic acid-water mixture containing water in an amount of 3-8% by weight, and the solubility of hydrogen iodide decreases as the water concentration decreases. This correlation increases the volatility of hydrogen iodide so that the amount of hydrogen iodide recovered in the tower overhead is reduced. Although hydrogen iodide has been shown to be corrosive, it may beneficially act as a catalyst under certain conditions of a given amount of hydrogen iodide. Such catalysts include the catalysts for forming dimethyl ether described in US Pat. No. 7,223,883 (which describes the advantages of forming dimethyl ether by a predetermined acetic acid separation method). The entire contents of the patent are incorporated herein by reference.

[0023] side draw stream may also contain one or more iodide C ₁ -C ₁₄ alkyl 0.1-6% by weight relative to the total weight of the side draw stream, also particularly include methyl iodide Good. Other alkyl iodides such as hexyl iodide may also be formed from carbonyl impurities such as acetaldehyde. The side withdrawal stream preferably contains 0.5 to 3% by weight of one or more iodide C ₁ -C ₁₄ alkyl. Due to the presence of water, the side withdrawal stream may also contain methyl acetate at a concentration of 0.1 to 6% by weight, for example 0.5 to 3% by weight, based on the total weight of the side withdrawal stream.

  [0024] Maintaining the desired concentration of methyl iodide in the vapor product stream is a measure of the water and methyl acetate concentrations in the vapor product fed to the first column, such as US Pat. No. 9,006,483. This is an improvement over other methods that focus on. Unlike water and methyl acetate, the loss of methyl iodide can represent a significant loss in cost due to its significant value. Therefore, in the present invention, a highly valuable catalyst promoter (for example, methyl iodide) can be recovered, but this may be separated and returned to the reactor.

[0025] The concentration of hydrogen iodide in the side withdrawal stream is determined by potentiometric titration using lithium acetate as the titration reagent. As another method, there is a method of indirectly obtaining the content of hydrogen iodide by calculation. For example, in U.S. Patent Publication No. 2013/0310603, the iodide ion concentration derived from iodide salt forms (including iodides derived from cocatalysts and metal iodides) is the total concentration of iodide ions (I ⁻ ). It is shown that the iodide ion concentration may be calculated by subtracting from. Such indirect calculation techniques are usually inaccurate, and the actual ion concentration measurement method is inaccurate, so that the actual hydrogen iodide concentration is not sufficiently shown. Also, this indirect calculation technique does not account for other iodide forms. The reason for this is that measuring metal cations assumes that all of these cations bind only to iodide anions, but this is incorrect, and in fact these metal cations are acetate anions. This is because it may bind to other anions such as catalyst anions. On the other hand, the direct measurement of the hydrogen iodide concentration according to the present invention can reflect the actual hydrogen iodide concentration in the system, and has an advantage that an accuracy as low as 0.01% can be obtained.
Reaction process
[0026] An exemplary reaction and acetic acid recovery system 100 is shown in FIG. As shown in the figure, a methanol-containing feed stream 101 and a carbon monoxide-containing feed stream 102 are directed to a liquid phase carbonylation reactor 105 to perform a carbonylation reaction to form acetic acid.

  [0027] The methanol-containing feed stream 101 may include at least one selected from the group consisting of methanol, dimethyl ether, and methyl acetate. The methanol-containing feed stream 101 may be partially derived from a new supply or may be recycled from the system. At least some of the methanol and / or reactive derivatives thereof are converted to methyl acetate in a liquid reaction medium by an esterification reaction with acetic acid.

  [0028] The usual reaction temperature for carbonylation is 150-250 ° C. A preferred temperature range is 180-225 ° C. The carbon monoxide partial pressure in the reactor may vary greatly, but is usually 2-30 atm, for example 3-10 atm. The hydrogen partial pressure in the reactor is usually 0.05 to 2 atm, for example 0.25 to 1.9 atm. Due to the partial pressure of by-products and the vapor pressure of the liquid contained, the total pressure in the reactor is in the range of 15-40 atm. The production rate of acetic acid may be 5 to 50 mol / L · h, for example 10 to 40 mol / L · h, preferably about 15 to 35 mol / L · h.

  [0029] The carbonylation reactor 105 is preferably a stirred vessel or bubble column vessel with or without a stirrer. In this, the content of the reaction liquid or slurry is maintained at a predetermined value, preferably automatically, and preferably substantially constant during normal operation. If necessary, fresh methanol, carbon monoxide, and sufficient water are continuously introduced into the carbonylation reactor 105 to maintain a suitable concentration in the reaction medium.

[0030] The metal catalyst may comprise a Group VIII metal. Suitable Group VIII catalysts include rhodium catalysts and / or iridium catalysts. When using a rhodium catalyst, as is well known in the _{art, [Rh (CO) 2 I} 2] - any suitable form of rhodium catalyst as rhodium equilibrium mixture containing anions present in the catalyst solution May be added. The iodide salt that may be maintained in the reaction mixture of the methods described herein may be in the form of an alkali metal, alkaline earth metal, quaternary ammonium, a soluble salt of a phosphonium salt, or a mixture thereof. Good. In some embodiments, the catalyst co-promoter is lithium iodide, lithium acetate, or a mixture thereof. The salt co-promoter may be added as a non-iodide salt that produces an iodide salt. The iodide catalyst stabilizer may be introduced directly into the reaction system. Alternatively, the iodide salt may be generated in-situ. This is because, under the operating conditions of the reaction system, a wide range of non-iodide salt precursors react with methyl iodide or iodohydroacid in the reaction medium to produce the corresponding co-promoted iodide salt stabilizer. is there. See US Pat. Nos. 5,001,259, 5,026,908, 5,144,068, and 7,005,541 for details on rhodium catalyst and iodide salt formation. The entire contents of which are incorporated herein by reference. Carbonylation of methanol using iridium catalysts is well known and is generally described in U.S. Pat. Nos. 5,942,460, 5,932,764, 5,883,295, 5,877,348, 5, 877,347 and 5,696,284. The entire contents of which are incorporated herein by reference.

  [0031] Halogen-containing catalyst promoters in the catalyst system include alkyl halides, aryl halides, and organic halides such as halogenated substituted alkyls or halogenated substituted aryls. The halogen-containing catalyst promoter is preferably present in the form of an alkyl halide. More preferably, the halogen-containing catalyst promoter is present in the form of an alkyl halide having an alkyl radical corresponding to the alkyl radical of the carbonylated feed alcohol. Thus, in the carbonylation of methanol to acetic acid, the halide promoter includes methyl halide, more preferably methyl iodide. In one aspect, the methyl iodide concentration in the steam product stream is maintained at a value of from 24% to less than 36% by weight. In one aspect, the methyl iodide concentration of the reaction medium may be 7 wt% or less, such as 4-7 wt%.

  [0032] The reaction medium components are maintained within specified limits to ensure a sufficient amount of acetic acid is produced. The reaction medium contains, for example, a metal catalyst such as a rhodium catalyst at a concentration of 200 to 3000 wppm, such as 800 to 3000 wppm, or 900 to 1500 wppm. The water concentration in the reaction medium is maintained at 15 wt% or less, such as 0.1 wt% to 14 wt%, 0.2 wt% to 10 wt%, or 0.25 wt% to 5 wt%. The reaction is carried out under low water conditions, and the reaction medium contains 0.1 to 4.1% by weight of water, for example 0.1 to 3.1% by weight, or 0.5 to 2.8% by weight. It is preferable. The methyl iodide concentration in the reaction medium is maintained at 3-20 wt%, 4-13.9 wt%, or 4-7 wt%. The concentration of an iodide salt such as lithium iodide in the reaction medium is maintained at 1 to 25 wt%, such as 2 to 20 wt%, or 3 to 20 wt%. The concentration of methyl acetate in the reaction medium is maintained at 0.5-30% by weight, such as 0.3-20% by weight, or 0.6-4.1% by weight. The following amounts are based on the total weight of the reaction medium. The concentration of acetic acid in the reaction medium is generally greater than 30% by weight, for example greater than 40% by weight or greater than 50% by weight.

  [0033] In one embodiment, the ester concentration in the reaction medium consisting of the desired carboxylic acid, an alcohol, preferably the alcohol used for carbonylation, and another iodide ion in addition to the iodide ion present as hydrogen iodide. By maintaining the above, a desired reaction rate can be obtained even when the water concentration is low. The desired ester is methyl acetate. The other iodide ion is desirably an iodide salt, and lithium iodide (LiI) is preferred. At low water concentrations, methyl acetate and lithium iodide act as kinetic promoters only when these components are present in relatively high concentrations, respectively, and promote when both of these components are present simultaneously. Was found to increase.

  [0034] The carbonylation reaction of methanol to the acetic acid product is carried out at a temperature and pressure conditions suitable to form the carbonylated product, a rhodium catalyst, a methyl iodide (MeI) promoter, methyl acetate (MeAc), and It may be carried out by contacting carbon monoxide gas supplied by bubbling with methanol to an acetic acid solvent reaction medium containing another soluble iodide salt. In general, what is important is the concentration of iodide ion in the catalyst system, not the concentration of cation binding to iodide, and if the iodide is at a given molar concentration, the nature of the cation is determined by the iodide concentration. It is recognized that it is not as important as the effect. Any metal iodide salt or any organic cation or other cationic iodide salt provided that the salt is sufficiently soluble in the reaction medium to provide the desired amount of iodide. An iodide salt of a cation (which may be a tertiary or quaternary cation), for example based on an amine or phosphine compound, may also be maintained in the reaction medium. When the iodide is a metal salt, from the Group IA and IIA metals of the periodic table as described in “Chemical and Physical Handbook” 2002-03 (83rd edition) published by the Cleveland CRC Press, Ohio A metal iodide salt selected from the group consisting of In particular, alkali metal iodide is useful, and lithium iodide is particularly preferable. In the low water carbonylation step, other iodide ions are present in the catalyst solution in addition to the iodide ions present as hydrogen iodide in an amount such that the total concentration of iodide ions is 1 to 25% by weight. Also, methyl acetate is generally present in an amount of 0.5-30% by weight and methyl iodide is generally present in an amount of 1-25% by weight. The rhodium catalyst is generally present in an amount of 200 to 3000 wppm.

  [0035] In a normal carbonylation process, carbon monoxide may be continuously introduced into the carbonylation reactor, preferably under a stirrer, and the contents may be stirred using the stirrer. It is preferable that the feed gas is sufficiently dispersed throughout the reaction solution by this stirring means. It is desirable to discharge the exhaust stream 106 from the reactor 105 to prevent accumulation of gas by-products and to maintain a carbon monoxide partial pressure set at a predetermined total pressure in the reactor. The temperature of the reactor may be controlled and carbon monoxide is fed at a rate sufficient to maintain the desired total pressure in the reactor. A stream 113 containing a liquid reaction medium is sent out of the reactor 105.

  [0036] The acetic acid production system preferably includes a separation system 108 that is used to recover acetic acid and recycle the metal catalyst, methyl iodide, methyl acetate, and other system components within the carbonylation process. One or more recycle streams may be mixed before being introduced into the reaction system. The reaction system includes a reactor and a flash vessel. The separation system also preferably controls the carbonylation reactor and the water and acetic acid content of the entire system to facilitate the removal of permanganate reducing compounds (PRC). PRC can include acetaldehyde, acetone, methyl ethyl ketone, butyraldehyde, crotonaldehyde, 2-ethylcrotonaldehyde, 2-ethylbutyraldehyde, and their aldol condensates.

  [0037] The reaction medium is removed from the carbonylation reactor at a rate sufficient to maintain a constant level in the carbonylation reactor 105 and fed to flash vessel 110 via stream 113. The reactor 105 and the flash vessel 110 constitute a reaction system together with related pumps, exhaust ports, pipes and valves. The flash separation may be performed at a temperature of 80 ° C. to 280 ° C. and an absolute pressure of 0.25 to 10 atm, more preferably 100 ° C. to 260 ° C. and an absolute pressure of 0.3 to 10 atm. In one aspect, the flash vessel may be operated under a lower pressure than the reactor. In the flash vessel 110, as described herein, the reaction medium is separated in a flash separation step to obtain a vapor product stream 112 containing acetic acid and methyl iodide and a liquid recycle stream 111 containing a catalyst-containing solution.

  [0038] The liquid recycle stream 111 includes acetic acid, metal catalysts, corrosive metals, and various other compounds. In one aspect, the liquid recycle stream is 60-90 wt% acetic acid, 0.01-0.5 wt% metal catalyst, 10-2500 wppm corrosive metal (e.g., nickel, iron, chromium, etc.), 5-20 % By weight lithium iodide, 0.5-5% by weight methyl iodide, 0.1-5% by weight methyl acetate, 0.1-8% by weight water, 1% by weight or less acetaldehyde (e.g. 0001 to 1 wt% acetaldehyde), and 0.5 wt% or less hydrogen iodide (eg 0.0001 to 0.5 wt% hydrogen iodide).

  [0039] Each flow rate of the steam product stream 112 and the liquid recycle stream 111 may vary, and in an exemplary embodiment, 15% to 55% of the flow to the flash vessel 110 is removed as the steam product stream 112; 45% to 85% is removed as liquid recycle stream 111. The catalyst-containing solution is mostly acetic acid containing a metal catalyst such as rhodium and / or iridium and an iodide salt, and may contain smaller amounts of methyl acetate, methyl iodide, and water. As shown in FIG. Prior to returning the liquid recycle stream to the reactor, as described in US Pat. No. 5,731,252, the entire contents of which are incorporated herein by reference, the slip stream is ionized. Any entrained corrosive metal may be removed by passing through a corrosive metal removal bed such as an exchange bed. Also, as described in US Pat. No. 8,697,908 (the entire contents of which are incorporated herein by reference), a corrosive metal removal bed is used to remove nitrogen compounds such as amines. May be.

[0040] In addition to acetic acid, methyl iodide, and acetaldehyde, the vapor product stream 112 may also include methyl acetate, water, hydrogen iodide, and other PRCs such as crotonaldehyde. The dissolved gas sent from the reactor 105 and supplied to the flash vessel 110 contains a portion of carbon monoxide, but may contain gas by-products such as methane, hydrogen, and carbon dioxide. Such dissolved gas is delivered from the flash vessel 110 as part of the vapor product stream 112. In one aspect, carbon monoxide in the exhaust stream 106 may be supplied to the bottom of the flash vessel 110 to enhance rhodium stability.
Acetic acid recovery
[0041] The distillation and recovery of acetic acid is not particularly limited for the purposes of the present invention. As shown in FIG. 1, a vapor product stream 112 containing less than 24-36% by weight methyl iodide is charged to a first column 120 (also referred to as a light fractionation column). In one aspect, the vapor product stream 112 is in addition to acetic acid, methyl acetate, water, methyl iodide, and acetaldehyde, as well as other impurities (such as hydrogen iodide) and / or by-products (such as crotonaldehyde and / or propionic acid). )including. Distillation results in a low boiling overhead vapor stream 122, a purified acetic acid product (preferably removed via side draw stream 123), and a high boiling residue stream 121. Most of the acetic acid is removed to the side draw stream 123, but it is preferred that little or no acetic acid is recovered from the high boiling residue stream 121.

  [0042] In one aspect, the low boiling overhead vapor stream 122 comprises more than 5 wt% water, such as more than 10 wt% water, or more than 25 wt% water, and no more than 80 wt% water. Also good. In terms of range, the low boiling overhead vapor stream 112 may include 5 wt% to 80 wt%, such as 10 wt% to 70 wt%, or 25 wt% to 60 wt% water. If the water concentration is reduced to less than 5% by weight, the acetic acid recycle stream generally returned to the reaction system increases and the recycle stream of the entire purification system increases, which is not preferable. Low boiling overhead vapor stream 122 may also contain carbonyl impurities such as methyl acetate, methyl iodide, and PRC in addition to water. These are preferably concentrated in the overhead vapor stream and removed from the acetic acid in the side draw stream 123.

  [0043] As shown, the low boiling overhead vapor stream 122 is preferably condensed and fed to an overhead phase separation unit, shown as an overhead decanter 124. Maintaining conditions so that the low-boiling overhead vapor stream 122 once condensed in the decanter 124 is separated into two phases, a light liquid phase 133 (also referred to as an aqueous phase) and a heavy liquid phase 134 (also referred to as an organic phase). Is desirable. Off-gas components may be exhausted from decanter 124 via line 132. Although the specific composition of the light liquid phase 133 can vary widely, some preferred compositions are shown in Table 1 below.

  [0044] The concentration of components (such as water and / or hydrogen iodide) in the side draw stream 123 may be controlled by the recycling rate of the light liquid phase 133 to the reaction system. Reflux ratio of the light liquid phase 133 to the first column via the line 135 (heavy liquid phase 134 (whether or not all recycled) and the light liquid phase 133 are sent from the top of the column 120. The mass flow rate of the reflux liquid divided by the total mass flow rate) is preferably 0.05 to 0.4, for example 0.1 to 0.35, or 0.15 to 0.3. In one aspect, it may be preferred that the number of theoretical plates between the side draw and the top of the first column is greater than 5, for example greater than 10, to reduce the reflux ratio. In one aspect, a flow valve and / or a flow monitor (not shown) may be used to control the reflux liquid in line 135 and the recycle stream in line 136.

  [0045] In one aspect, the recycle rate of the light liquid phase in line 136 to the reaction system is no more than about 20% of the total amount of light liquid phase 133 condensed from the overhead of the first column, such as no more than about 10%. It is. In terms of range, the light liquid phase recycle rate in line 136 is 0-20% of the total amount of light liquid phase 133 condensed from the overhead of the first tower, such as 0.5-20%, or 1- It may be 10%. The remaining portion may be used as a reflux liquid in a light fractionator, or may be supplied to a PRC removal system. For example, the recycle stream in line 136 may be mixed with liquid recycle stream 111 and returned to reactor 105. In one aspect, the recycle stream in line 136 may be mixed with other streams that are recycled to the reaction system, such as reactor 105 or flash vessel 110, for example. If the condensation overhead stream 138 from the drying tower 125 is phase separated into an aqueous phase and an organic phase, it may be preferable to mix the recycle stream in line 136 with the aqueous phase. Alternatively, all or at least a portion of the recycle stream in line 136 may be mixed with the heavy liquid phase 134 and / or the organic phase from the overhead stream 138.

  [0046] A carbonyl impurity such as acetaldehyde in the system is reacted with an iodide catalyst promoter to form an alkyl iodide such as ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, and the like. Also good. In addition, since most of the impurities are derived from acetaldehyde, it is desirable to remove carbonyl impurities from the light liquid phase. Thus, a portion (preferably an aliquot) of the light liquid phase 133 may be separated in stream 142 and charged into acetaldehyde or PRC removal system 140 to recover methyl iodide and methyl acetate. As shown in Table 1, the light liquid phase 133 contains PRC, and the process may include removing carbonyl impurities such as acetaldehyde that impair the quality of the acetic acid product. These carbonyl impurities are described in U.S. Patent Nos. 6,143,930, 6,339,171, 7,223,883, 7,223,886, 7,855,306, 7,884,237, It may be removed by a suitable impurity removal tower or impurity absorber described in US Pat. No. 8,889,904 and US Patent Publication No. 2006/0011462. The entire contents of these patents are incorporated herein by reference.

  [0047] In some embodiments, all or part of the light liquid phase 133 and / or the heavy liquid phase 134 may be charged to the PRC removal system as described above. When it is preferred to control the reflux ratio of the light liquid phase 133 and the portion charged into the PRC removal system so that the hydrogen iodide in the side draw stream 123 and the water recycled to the reactor are in the desired balance There is.

  [0048] In some embodiments, all or a portion of the heavy liquid phase 134 containing more methyl acetate and methyl iodide than the light liquid phase 133 may be recycled to the reactor 105 and / or the first The column 120 may be refluxed. Carbonyl impurities may be further removed from the heavy liquid phase 134 in the same manner as described for the light liquid phase 133.

  [0049] In certain embodiments, the method comprises one or more on-line analyzers for measuring the concentration of various components in different streams. For example, a sample stream such as a sample exhaust stream may be supplied to an online analyzer (not shown) to determine the hydrogen iodide concentration in the side withdrawal stream 123 using the online analyzer.

  [0050] Preferably, the acetic acid removed via the side draw stream 123 is further purified, such as in a second column 125 (also referred to as a drying column). The second column separates the side draw stream 123 into an overhead stream 126 containing mainly water and a bottom stream 127 containing mainly acetic acid. Acetic acid may be recovered as a side stream near the bottom of the second column 125. Overhead stream 126 may contain 50 to 75 weight percent water. Residual methyl acetate and methyl iodide are also removed from the side draw stream and concentrated in the overhead stream of the drying tower. The drying tower bottom stream 127 preferably comprises acetic acid or consists essentially of acetic acid. For the purposes of the present invention, bottom stream 127 may be withdrawn to the residue of column 125 or withdrawn near the bottom of column 125. In a preferred embodiment, the bottom stream 127 of the drying tower contains more than 90% by weight acetic acid, such as more than 95% or 98% by weight acetic acid. The bottom stream 127 of the drying tower may be further processed, such as passing through an ion exchange resin, before being stored or transported for commercial use.

  [0051] Similarly, the overhead stream 126 from the second column 125 contains reaction components such as methyl iodide, methyl acetate, water, etc., but it is preferred to retain these reaction components in the process. As shown, overhead stream 126 is condensed by a heat exchanger to stream 138, which is recycled to reactor 105 and / or refluxed to second column 125. Off-gas components may be discharged from the condensed low boiling overhead vapor stream 126 via line 137. Similar to the condensed low boiling overhead vapor stream from the first column 120, the condensed overhead stream 138 may also be separated into a light and heavy liquid phase. If desired, these phases may be recycled or refluxed to maintain the desired component concentrations in the reaction medium.

  [0052] In particular, these lines may be fed to the scrubber to recover residual liquid from the exhaust streams of lines 106, 132, 137. The scrubber is operated with cold methanol and / or acetic acid to remove methyl acetate and methyl iodide. A suitable scrubber is described in US Pat. No. 8,318,977, the entire contents of which are hereby incorporated by reference.

[0053] The distillation column of the present invention may be a conventional distillation column, for example, in particular a plate column, a packed column. Materials used to form the distillation column include, but are not limited to, glass, metal, ceramics, and other suitable materials. In the case of a plate column, the number of theoretical plates depends on the components to be separated, and each column can be 50 plates or less, for example, 5 to 50 plates, or 7 to 35 plates.
Guard bed
[0054] If the total concentration of iodide in the purified acetic acid product is low, such as 5 wppm or less, such as 1 wppm or less, the guard bed can be used to remove iodide. The removal of residual iodide using one or more guard beds greatly improves the quality of the purified acetic acid product. A carboxylic acid stream (eg, an acetic acid stream) contaminated with halides and / or corrosive metals may be contacted with the ion exchange resin composition of the present invention under various operating conditions. The ion exchange resin composition is preferably provided in the guard bed. Purifying a contaminated carboxylic acid stream using a guard bed is well documented in the art, for example, U.S. Pat. Nos. 4,615,806, 5,653,853, 5,731,252, And 6,225,498, the entire contents of which are hereby incorporated by reference. Purifying a contaminated carboxylic acid stream using a guard bed, for example, generally contacts the contaminated liquid carboxylic acid stream with an ion exchange resin composition, which ion exchange resin composition is provided in the guard bed. Is preferred. For example, a halide contaminant such as an iodide contaminant is reacted with a metal to form metal iodide. In some embodiments, hydrocarbon moieties that may bind iodide, such as a methyl group, may esterify the carboxylic acid. For example, in the case of acetic acid contaminated with methyl iodide, methyl acetate is produced as a byproduct of iodide removal. This esterification formation usually does not deleteriously affect the treated carboxylic acid stream.

  [0055] The pressure in the contacting step is mainly limited by the physical strength of the resin. In one aspect, the contacting is performed at a pressure in the range of 0.1 MPa to 1 MPa, such as 0.1 MPa to 0.8 MPa, or 0.1 MPa to 0.5 MPa. However, for convenience, it is preferred to treat both the contaminated carboxylic acid stream as a liquid by defining both pressure and temperature. Thus, for example, in operation at atmospheric pressure, which is generally preferred from an economic point of view, the temperature may range from 17 ° C. (freezing point of acetic acid) to 118 ° C. (boiling point of acetic acid). It is within the purview of those skilled in the art to determine equivalent ranges for product streams containing other carboxylic acid compounds. It is preferred to keep the temperature of the contact process relatively low to minimize resin degradation. In one aspect, the contacting step is performed at a temperature in the range of 25 ° C to 120 ° C, such as 25 ° C to 100 ° C, or 50 ° C to 100 ° C. Some cationic macroreticular resins usually begin to degrade at temperatures of 150 ° C. (due to the reaction mechanism of acid-catalyzed aromatic desulfonation). Carboxylic acids having 5 or less carbon atoms, such as 3 or less, remain liquid at temperatures in this range. Therefore, the temperature at the time of contact must be kept lower than the deterioration temperature of the resin used. In some embodiments, the operating temperature is kept below the temperature limit of the resin to match the liquid phase operation and the desired reaction rate for halide removal.

  [0056] The configuration of the guard bed in the acetic acid purification system may vary widely. For example, a guard floor may be provided after the drying tower. In addition or alternatively, a guard may be provided after the heavy removal tower or finishing tower. It is preferred to provide a guard bed at a location where the temperature of the acetic acid product stream is low, for example below 120 ° C or below 100 ° C. In addition to the advantages described above, when the operating temperature is low, there is less corrosion than when the operating temperature is high. When the operating temperature is low, formation of corrosive metal contaminants that may reduce the total life of the resin as described above is suppressed. Further, when the operating temperature is low, the corrosion is suppressed, so there is an advantage that the container does not need to be made of an expensive corrosion-resistant metal. For example, a lower grade metal such as general stainless steel may be used.

  [0057] In one aspect, the flow rate at the guard bed ranges from 0.1 bed volumes per hour (BV / hr) to 50 BV / hr, such as 1 BV / hr to 20 BV / hr, or 6 BV / hr. hr-10BV / hr may be sufficient. The bed volume of the organic medium is the volume of the medium equal to the volume occupied by the resin bed. A flow rate of 1 BV / hr means that an amount of organic liquid equal to the volume occupied by the resin bed passes through the resin bed in one hour.

[0058] To avoid depleting the resin with a purified acetic acid product having a high total iodide concentration, in one aspect, when the total iodide concentration of the purified acetic acid product is 5 wppm or less, such as preferably 1 wppm or less, Purified acetic acid product in bottom stream 127 is contacted with the guard bed. In one exemplary aspect, the total iodide concentration of the purified acetic acid product may be from 0.01 wppm to 5 wppm, such as from 0.01 wppm to 1 wppm. If the iodide concentration exceeds 5 wppm, re-treatment of non-standard acetic acid may be required. The total iodide concentration include iodides from both inorganic sources such as organic sources, and hydrogen iodide, such as iodide C ₁ -C ₁₄ alkyl. As a result of the treatment on the guard bed, a purified acetic acid composition is obtained. In one aspect, the purified acetic acid composition comprises less than 100 wppb iodide, such as less than 90 wppb, less than 50 wppb, or less than 25 wppb. In one aspect, the purified acetic acid composition comprises less than 1000 wppb corrosive metal, such as less than 750 wppb, less than 500 wppb, or less than 250 wppb. With respect to the range, the purified acetic acid composition may contain 0-100 wppb, such as 1-50 wppb iodide and / or 0-1000 wppb, such as 1-500 wppb corrosive metal. In other embodiments, the guard bed removes at least 25 wt%, such as at least 50 wt%, or at least 75 wt% iodide from the crude acetic acid product. In one aspect, the guard bed removes at least 25 wt%, such as at least 50 wt%, or at least 75 wt% corrosive metal from the crude acetic acid product.

  [0059] Although the present invention has been described in detail, those skilled in the art will readily appreciate variations within the spirit and scope of the present invention. In view of the above description, all references and disclosures related to relevant knowledge in the field, [Background Art] and [Mode for Carrying Out the Invention] are incorporated herein by reference. It is. It should also be understood that various features recited in aspects and aspects of the present invention, the following description and / or the appended claims may be combined or interchanged in whole or in part. May be. Those skilled in the art will appreciate that, in the above description of various aspects, aspects referring to other aspects may be combined appropriately with other aspects. Further, those skilled in the art will appreciate that the above description is illustrative only and is not intended to limit the invention.

[0060] The invention will be better understood by the following non-limiting examples.
Example 1
[0061] A reactor containing rhodium (about 900 ppm by weight), methyl iodide (about 9% by weight), lithium iodide, water, and methyl acetate as a rhodium carbonyl iodide compound is charged with methanol, carbon monoxide, and hydrogen. Feed and maintain a hydrogen partial pressure of at least about 0.27 atm (ie, at least about 4 psi). The water concentration was less than 4% by weight. The reactor was maintained at a temperature between about 190 ° C. and 200 ° C. and operated at a pressure greater than about 28 atm (ie, greater than about 400 psig). A liquid level control device that senses the liquid level in the reactor continuously removed the liquid reaction medium and supplied it to a single-stage flash vessel operating at about 150 ° C. and about 3.2 atm (ie, 32.3 psig). . The carbon monoxide recovered from the exhaust port of the reactor was sprayed on the reaction medium taken out and then put into a flash container. About 28% of the reaction medium is delivered as a vapor product stream and the remaining amount is returned to the reactor as a liquid. The steam product stream was removed at a temperature of about 50 ° C. The composition of the steam product stream was 66.35% by weight acetic acid, 25.01% by weight methyl iodide, 5.97% by weight methyl acetate, 1.53% by weight water, 0.1% by weight acetaldehyde, And less than 1% by weight of hydrogen iodide.

  [0062] The steam product stream was fed to a light fractionator to obtain overhead and side draw streams. As a typical example, a sufficient amount of a side withdrawal sample was titrated with 0.01 M lithium acetate in acetone (50 ml) to determine the HI concentration in the side withdrawal stream. The end point was determined in a dynamic equivalent point titration mode using a pH electrode with a titrator Metrohm 716 DMS Titrino. Based on the consumption amount of the lithium acetate titration reagent, the HI concentration was calculated by weight% from the following formula.

[0063] A side draw stream composition sample containing about 1.9 wt% water was tested using this HI titration method. When the light liquid phase from the overhead light fraction was recycled to the reaction system, the HI concentration changed from 50 wppm to 300 wppm. Thus, by maintaining the methyl iodide concentration in the steam product stream, the HI concentration in the light fractionator could be controlled.
Example 2
[0064] The reaction of Example 1 was repeated except that the methyl iodide in the reaction medium was about 12 wt% and the pressure in the flash vessel was slightly lower at about 3.1 atm (ie, 30.8 psig). About 31% of the reaction medium was delivered as a vapor product stream and the remaining amount was returned to the reactor as a liquid. The composition of the steam product stream was 61.97 wt% acetic acid, 30.34 wt% methyl iodide, 5.05 wt% methyl acetate, 1.54 wt% water, 0.09 wt% acetaldehyde, And less than 1% by weight of hydrogen iodide.

  [0065] A portion of the light liquid phase from the light fraction overhead was recycled to the reaction system. The side draw stream contained 1.5 wt% water and less than 25 wppm HI, with the balance containing acetic acid, methyl acetate, and methyl iodide. The HI concentration was too low to be measured directly by titration. Other cations present in the side withdrawal stream made direct measurement of HI difficult. The total amount of inorganic iodide, ie the maximum possible total HI amount, was directly measured. Other inorganic iodides may include corrosive metal iodides in addition to lithium iodide. Example 2 also had the advantage that by maintaining the methyl iodide concentration in the vapor product stream, the HI concentration in the light fractionator and ultimately in the side draw stream could be controlled.

[0065] A portion of the light liquid phase from the light fraction overhead was recycled to the reaction system. The side draw stream contained 1.5 wt% water and less than 25 wppm HI, with the balance containing acetic acid, methyl acetate, and methyl iodide. The HI concentration was too low to be measured directly by titration. Other cations present in the side withdrawal stream made direct measurement of HI difficult. The total amount of inorganic iodide, ie the maximum possible total HI amount, was directly measured. Other inorganic iodides may include corrosive metal iodides in addition to lithium iodide. Example 2 also had the advantage that by maintaining the methyl iodide concentration in the vapor product stream, the HI concentration in the light fractionator and ultimately in the side draw stream could be controlled.
The description of the scope of claims at the time of filing is shown below.
[Claim 1]
In a flash vessel, the reaction medium is a liquid recycle stream and 45-75 wt% acetic acid, 24 wt% to less than 36 wt% methyl iodide, 9 wt% methyl acetate, 15 wt% water, Separating into a steam product stream comprising 005 to 1% by weight of acetaldehyde and 1% by weight or less of hydrogen iodide, and distilling at least a portion of the steam product stream in a first column to produce acetic acid and 300 wppm A process for producing acetic acid comprising obtaining an acetic acid product stream comprising hydrogen iodide and an overhead stream comprising methyl iodide, water and methyl acetate.
[Claim 2]
The steam product stream comprises 55-75 wt% acetic acid, 24-35 wt% methyl iodide, 0.5-8 wt% methyl acetate, 0.5-14 wt% water, 0.01-0 The method of claim 1 comprising .8 wt% acetaldehyde and 0.5 wt% or less hydrogen iodide.
[Claim 3]
The steam product stream comprises 60-70 wt% acetic acid, 25-35 wt% methyl iodide, 0.5-6.5 wt% methyl acetate, 1-8 wt% water, 0.01-0 The method of claim 1 comprising .7 wt% acetaldehyde and 0.1 wt% or less hydrogen iodide.
[Claim 4]
The method of claim 1, wherein the acetic acid product stream comprises no more than 50 wppm hydrogen iodide.
[Claim 5]
The process of claim 1, wherein the acetic acid product stream comprises 0.1 to 6 wt% methyl iodide.
[Claim 6]
The method of claim 1, wherein the acetic acid product stream comprises 0.1 to 6 wt% methyl acetate.
[Claim 7]
The process of claim 1 wherein the water concentration in the acetic acid product stream is maintained at 1-9 wt%.
[Claim 8]
The method according to claim 1, wherein the increase in the net production of water in the distillation step is 0.5% or less relative to the water concentration in the steam product stream supplied to the distillation step.
[Claim 9]
The liquid recycle stream comprises 0.01-0.5 wt% metal catalyst, 5-20 wt% lithium iodide, 10-2500 wppm corrosive metal, 60-90 wt% acetic acid, 0.5-5 % By weight methyl iodide, 0.1-5% by weight methyl acetate, 0.1-8% by weight water, 0.0001-1% by weight acetaldehyde, and 0.0001-0.5% by weight iodine. The process of claim 1 comprising hydrogen fluoride.
[Claim 10]
The method of claim 1, wherein the overhead stream is phase separated to form a light liquid phase and a heavy liquid phase.
[Claim 11]
The light liquid phase comprises 1 to 40 wt% acetic acid, 10 wt% or less methyl iodide, 1 to 50 wt% methyl acetate, 40 to 80 wt% water, 5 wt% or less acetaldehyde, and 2 wt% 11. The method of claim 10, comprising no more than% hydrogen iodide.
[Claim 12]
The light liquid phase is 15-25 wt% acetic acid, 1-5 wt% methyl iodide, 1-10 wt% methyl acetate, 60-75 wt% water, 0.1-0.7 wt% 11. The process of claim 10 comprising acetaldehyde and 0.001-0.5% by weight hydrogen iodide.
[Claim 13]
In a flash vessel, the reaction medium is a liquid recycle stream and 45-75 wt% acetic acid, 24 wt% to less than 36 wt% methyl iodide, 9 wt% methyl acetate, 15 wt% water, Separating into a steam product stream comprising 005 to 1% by weight of acetaldehyde and 1% by weight or less of hydrogen iodide, and distilling at least a portion of the steam product stream in a first column to produce acetic acid and 0 A process for producing acetic acid comprising obtaining an acetic acid product stream comprising 1 to 6% by weight methyl iodide and an overhead stream comprising methyl iodide, water and methyl acetate.
[Claim 14]
The steam product stream comprises 55-75 wt% acetic acid, 24-35 wt% methyl iodide, 0.5-8 wt% methyl acetate, 0.5-14 wt% water, 0.01-0 The method of claim 1 comprising .8 wt% acetaldehyde and 0.5 wt% or less hydrogen iodide.
[Claim 15]
The method of claim 1, wherein the acetic acid product stream comprises 300 wppm or less of hydrogen iodide.
[Claim 16]
The method of claim 1, wherein the acetic acid product stream comprises 0.1 to 6 wt% methyl acetate.
[Claim 17]
The process of claim 1 wherein the water concentration in the acetic acid product stream is maintained at 1-9 wt%.
[Claim 18]
The liquid recycle stream comprises 0.01-0.5 wt% metal catalyst, 5-20 wt% lithium iodide, 10-2500 wppm corrosive metal, 60-90 wt% acetic acid, 0.5-5 % By weight methyl iodide, 0.1-5% by weight methyl acetate, 0.1-8% by weight water, 0.0001-1% by weight acetaldehyde, and 0.0001-0.5% by weight iodine. The process of claim 1 comprising hydrogen fluoride.
[Claim 19]
45-75 wt% acetic acid, 24 wt% to less than 36 wt% methyl iodide, 9 wt% or less methyl acetate, 15 wt% or less water, 0.005-1 wt% acetaldehyde, and 1 wt% Distilling a mixture containing the following hydrogen iodide to form an overhead stream containing methyl iodide and a side withdrawal stream containing acetic acid, and condensing the overhead stream to form a separate liquid phase A process for producing acetic acid.
[Claim 20]
20. The method of claim 19, wherein the water concentration in the side draw stream is maintained at 1-3 wt% and the hydrogen iodide concentration is maintained at 300 wppm or less.

Claims (20)

In a flash vessel, the reaction medium is a liquid recycle stream and 45-75 wt% acetic acid, 24 wt% to less than 36 wt% methyl iodide, 9 wt% methyl acetate, 15 wt% water, Separating into a steam product stream comprising 005 to 1% by weight of acetaldehyde and 1% by weight or less of hydrogen iodide, and distilling at least a portion of the steam product stream in a first column to produce acetic acid and 300 wppm A process for producing acetic acid comprising obtaining an acetic acid product stream comprising hydrogen iodide and an overhead stream comprising methyl iodide, water and methyl acetate.   The steam product stream comprises 55-75 wt% acetic acid, 24-35 wt% methyl iodide, 0.5-8 wt% methyl acetate, 0.5-14 wt% water, 0.01-0 The method of claim 1 comprising .8 wt% acetaldehyde and 0.5 wt% or less hydrogen iodide.   The steam product stream comprises 60-70 wt% acetic acid, 25-35 wt% methyl iodide, 0.5-6.5 wt% methyl acetate, 1-8 wt% water, 0.01-0 The method of claim 1 comprising .7 wt% acetaldehyde and 0.1 wt% or less hydrogen iodide.   The method of claim 1, wherein the acetic acid product stream comprises no more than 50 wppm hydrogen iodide.   The process of claim 1, wherein the acetic acid product stream comprises 0.1 to 6 wt% methyl iodide.   The method of claim 1, wherein the acetic acid product stream comprises 0.1 to 6 wt% methyl acetate.   The process of claim 1 wherein the water concentration in the acetic acid product stream is maintained at 1-9 wt%.   The method according to claim 1, wherein the increase in the net production of water in the distillation step is 0.5% or less relative to the water concentration in the steam product stream supplied to the distillation step.   The liquid recycle stream comprises 0.01-0.5 wt% metal catalyst, 5-20 wt% lithium iodide, 10-2500 wppm corrosive metal, 60-90 wt% acetic acid, 0.5-5 % By weight methyl iodide, 0.1-5% by weight methyl acetate, 0.1-8% by weight water, 0.0001-1% by weight acetaldehyde, and 0.0001-0.5% by weight iodine. The process of claim 1 comprising hydrogen fluoride.   The method of claim 1, wherein the overhead stream is phase separated to form a light liquid phase and a heavy liquid phase.   The light liquid phase comprises 1 to 40 wt% acetic acid, 10 wt% or less methyl iodide, 1 to 50 wt% methyl acetate, 40 to 80 wt% water, 5 wt% or less acetaldehyde, and 2 wt% 11. The method of claim 10, comprising no more than% hydrogen iodide.   The light liquid phase is 15-25 wt% acetic acid, 1-5 wt% methyl iodide, 1-10 wt% methyl acetate, 60-75 wt% water, 0.1-0.7 wt% 11. The process of claim 10 comprising acetaldehyde and 0.001-0.5% by weight hydrogen iodide. In a flash vessel, the reaction medium is a liquid recycle stream and 45-75 wt% acetic acid, 24 wt% to less than 36 wt% methyl iodide, 9 wt% methyl acetate, 15 wt% water, Separating into a steam product stream comprising 005 to 1% by weight of acetaldehyde and 1% by weight or less of hydrogen iodide, and distilling at least a portion of the steam product stream in a first column to produce acetic acid and 0 A process for producing acetic acid comprising obtaining an acetic acid product stream comprising 1 to 6% by weight methyl iodide and an overhead stream comprising methyl iodide, water and methyl acetate.   The steam product stream comprises 55-75 wt% acetic acid, 24-35 wt% methyl iodide, 0.5-8 wt% methyl acetate, 0.5-14 wt% water, 0.01-0 The method of claim 1 comprising .8 wt% acetaldehyde and 0.5 wt% or less hydrogen iodide.   The method of claim 1, wherein the acetic acid product stream comprises 300 wppm or less of hydrogen iodide.   The method of claim 1, wherein the acetic acid product stream comprises 0.1 to 6 wt% methyl acetate.   The process of claim 1 wherein the water concentration in the acetic acid product stream is maintained at 1-9 wt%.   The liquid recycle stream comprises 0.01-0.5 wt% metal catalyst, 5-20 wt% lithium iodide, 10-2500 wppm corrosive metal, 60-90 wt% acetic acid, 0.5-5 % By weight methyl iodide, 0.1-5% by weight methyl acetate, 0.1-8% by weight water, 0.0001-1% by weight acetaldehyde, and 0.0001-0.5% by weight iodine. The process of claim 1 comprising hydrogen fluoride. 45-75 wt% acetic acid, 24 wt% to less than 36 wt% methyl iodide, 9 wt% or less methyl acetate, 15 wt% or less water, 0.005-1 wt% acetaldehyde, and 1 wt% Distilling a mixture containing the following hydrogen iodide to form an overhead stream containing methyl iodide and a side withdrawal stream containing acetic acid, and condensing the overhead stream to form a separate liquid phase A process for producing acetic acid.   20. The method of claim 19, wherein the water concentration in the side draw stream is maintained at 1-3 wt% and the hydrogen iodide concentration is maintained at 300 wppm or less.

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